Thermally conductive coatings for light emitting devices

Abstract

A light emitting device, such as semiconductor laser diodes, superluminescent devices, semiconductor amplifiers and polymer-based light emitting devices, is provided with a coating that will increase the thermal conductivity at one or more facets of the device to provide for lowering the facet temperature during device operation to suppress the occurrence of temperature dependent facet degrading mechanisms and the catastrophic optical damage (COD) level of the light emitting device since these facet attributes are directly affected by temperature at the facet. In the preferred embodiment, the coating should have a thermal conductivity that is higher than the material of the light emitting device. The high thermal conductivity coating provides for an efficient transfer of heat away from the beam emission area of the front facet into regions adjacent to, i.e., above or below the active region of the device, such as layers of the device underlying the active region and the device substrate. If the coating material does not provide a sufficiently high level of thermal conductivity, then thermal resistance should be taken into consideration and the coating should be made thicker to achieve lower thermal resistance and, therefore, higher heat spreading toward lowering the facet temperature. In either case, the rate of heat transfer from the facet is enhanced so that the onset of higher temperature dependent facet degrading mechanisms and COD developing at the device facet are reduced or suppressed.

What is claimed is:  
     
       1. A light emitting device comprising: 
       a plurality of deposited layers with faces formed in plane transverse to the longitudinal extent of said layers forming longitudinal ends of the device, the device being fabricated from a material capable of producing light;  
       said light being emitted as a beam from at least one of said facets and generating heat thereat; and  
       a singe layer coating formed on at least one of said facets for transferring heat therefrom to increase the useful life of the device, said coating having a thickness near Nλ/(4n), where N is an odd integer greater than 1, so as to provide a facet reflectivity level substantially the same as a λ/(4n) thick layer but with improved heat transport quality, where λ is the oscillation wavelength of the device and n is the refractive index of the coating, and having a thermal conductivity higher than the thermal conductivity of the said device material.  
     
     
       2. The light emitting device of  claim 1  wherein the device material is a Group III-V material. 
     
     
       3. The light emitting device of  claim 2  wherein the device material comprises GaAs, AlGaAs, GaInP, GaInAsP, or AlGaInP. 
     
     
       4. The light emitting device of  claim 1  wherein the device material is a Group II-VI material. 
     
     
       5. The light emitting device of  claim 1  wherein the device material comprises light emitting polymers. 
     
     
       6. The light emitting device of  claim 1  wherein said coating comprises a single layer of SiC, BN, BeO,AlN, BP, MgO, B 2 O 3 , diamond or diamond-like carbon. 
     
     
       7. The light emitting device of  claim 1  wherein said coating comprises a bulk diamond material secured to said one facet. 
     
     
       8. The light emitting device of  claim 1  wherein the thickness of said layer is selected to provide, in combination, a reflectivity of 30% or less and to provide for thermal transport of heat away from the facet. 
     
     
       9. The light emitting device of  claim 1  wherein the thickness is selected to provide for lower thermal resistance so that said coating provides for a larger thermal transfer path under the conditions where said coating does not provide a sufficiently higher level of thermal conductivity compared to the thermal conductivity of the device material. 
     
     
       10. The light emitting device of  claim 9  herein said coating comprises a single layer of SiC, BN, BeO, AlN, BP, alumina, diamond or diamond-like carbon, B 2 O 3  or MgO. 
     
     
       11. The light emitting device of  claim 1  wherein said coating comprises a slab secured to said one facet, said slab comprising diamond, diamond-like carbon or AlN. 
     
     
       12. The light emitting device of  claim 1  where the device is mounted on a submount or substrate, said facet coating extending to said submount or substrate. 
     
     
       13. The light emitting dice of  claim 1  wherein said light emitting device comprises a semiconductor light emitting device or a polymer light emitting device. 
     
     
       14. The light emitting device of  claim 13  wherein said semiconductor light emitting device comprises a laser diode, a laser diode array, a superluminescent device or a semiconductor optical amplifier. 
     
     
       15. A light emitting laser device comprising: 
       laser beam emission area from at least one of its facets;  
       a coating of alumina formed on said one facet having a thickness near Nλ/(4n), where N is an odd integer greater than 1, so as to provide a facet reflectivity level substantially the same as λ/(4n) thick layer but with lower thermal resistance to improve the heat transport quality of the coating, where λ is the oscillation wavelength of the laser device and n is the refractive index of the coating.  
     
     
       16. The light emitting device of  claim 15  wherein the odd integer is chosen to be a small number.